1. Field of the Invention
The invention relates to a manufacturing method of an image forming apparatus, a manufacturing apparatus of an image forming apparatus, and the image forming apparatus manufactured by the manufacturing method.
2. Related Background Art
Hitherto, as electron emitting devices, mainly, two kinds of devices, i.e., a device using a thermionic emitting device and a device using a cold cathode electron emitting device, has been known. As cold cathode electron emitting devices, there are a field emission type (hereinafter, abbreviated as an "FE" type), a metal/insulating layer/metal type (hereinafter, abbreviated as an "MIM" type), a surface conducting type electron emitting device, and the like.
As an example of the FE type, there has been known a device disclosed in W. P. Dyke & W. W. Dolan, "Field Emission", Advances in Electron Physics, 8,89, 1956, C. A. Spindt, "Physical Properties of Thin-Film Field Emission Cathodes with Molybdenum Cones", J. Appl. Phys., 47,5248, 1976, or the like.
As an example of the MIM type, there has been known a device disclosed in C. A. Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32,646, 1961, or the like.
As an example of the surface conducting type electron emitting device, there has been known a device disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10,1290, 1965, or the like.
The surface conducting type electron emitting device uses a phenomenon in which an electron emission occurs by the supplying of a current to a thin film of small area formed on a substrate so as to be in parallel with the film surface. As a surface conducting type electron emitting device, there has been reported a device using a SnO.sub.2 thin film by Elinson et al., mentioned above, a device using an Au thin film [G. Dittmer, "Thin Solid Films", 9,317, 1972], a device using an In.sub.2 O.sub.3 /SnO.sub.2 thin film [M. Hartwell and C. G. Fonstad, IEEE Trans. ED Conf., 519, 1975], a device using a carbon thin film [Hisashi Araki, et al., Vacuum, Vol. 26, No. 1, pages 22, 1983], or the like.
As a typical device construction of those surface conducting type electron emitting devices, a device construction of M. Hartwell mentioned above is diagrammatically shown in FIGS. 7A and 7B.
In FIGS. 7A and 7B, reference numeral 71 denotes a substrate; 72 and 73 element electrodes; and 74 a conductive film made of a metal oxide thin film or the like formed in an H-shaped pattern by sputtering. An electron emitting portion 75 is formed by a current supplying process called a current supply forming, which will be explained hereinbelow. An interval L between the element electrodes in the diagram is set to 0.5 to 1 mm and W' is set to 0.1 mm.
Hitherto, in those surface conducting type electron emitting devices, generally, the electron emitting portion 75 is preliminarily formed by subjecting the conductive film 74 to the current supplying process called a current supply forming prior to performing an electron emission. That is, in the current supply forming, a DC voltage or a voltage of very moderately increased magnitude, for example, at a rate about 1 V/min, is applied across the conductive thin film 74 so that a current flows, thereby locally breaking, deforming, or degenerating the conductive thin film and forming the electron emitting portion 75 in an electrically high resistance state.
In the electron emitting portion 75, a crack occurs in a part of the conductive film 74, and an electron emission is performed from a portion near the crack. In the surface conducting type electron emitting device on which the current supply forming process has been performed, a voltage is applied to the conductive thin film 74 and a current is supplied to the device, thereby emitting electrons from the electron emitting portion 75.
In the surface conducting type electron emitting device, a method whereby carbon and/or a compound of carbon are formed in the electron emitting portion of the surface conducting type electron emitting device by a new manufacturing method called an activating step, thereby remarkably improving electron emitting characteristics, has been proposed (JP-A-7-235255).
According to the activating step, in the manufacturing method of the surface conducting type electron emitting device, a device in which a pair of electrodes and a conductive film are formed is put in a vacuum ambience and is subjected to a forming step, and thereafter, organic material gas having carbon is introduced into the vacuum ambience, and a pulse-like voltage which is properly selected is applied to the device for a few to several tens of minutes. According to this step, the characteristics of the electron emitting device, namely, an electron emission current Ie, remarkably increases and is improved while keeping unchanged a threshold value for the voltage.
However, in the image forming apparatus using the above conventional electron emitting device, there is a case where the following problems occur.
(1) In a large image forming apparatus, an electron source substrate (rear plate) on which a plurality of electron emitting devices are formed and a face plate on which a fluorescent body or the like is formed are positioned so as to keep desired relative positions, and are assembled and temporarily fixed at a predetermined distance of a few millimeters or less, and thereafter, the temperature is raised up to a temperature at which an adhering material such as frit glass or the like is softened, and pressure is applied so that those plates are adhered, together with a space between them thereby forming a vacuum envelope (this step is called a heat seal bonding step). However, since the distance between the electron source substrate and the face plate is short and the conductance of the gas is small, in an exhausting step in the image forming apparatus subsequent to the seal bonding step, it takes time to exhaust the space to an adequate degree of vacuum through an exhaust pipe or, if the exhausting step is finished in a short time, the degree of vacuum in the apparatus is low, or a pressure fluctuation occurs. There is, consequently, a case where a degree of vacuum which is necessary for stable electron emitting characteristics cannot be obtained.
Although a high positioning precision is required in the relative arrangement between the electron emitting device and the fluorescent body in order to prevent a color deviation or the like, there is a case where the necessary positional precision cannot be obtained due to the positional deviation or the like due to a thermal expansion in the seal bonding step or the softening of frit glass that is used for seal bonding. As a device in which they are seal bonded in the vacuum, a method of using rod glass of a low melting point and adhering and introducing into a vacuum apparatus has been disclosed in JP-A-6-196094. Even in this case, however, positional deviation during the frit melting cannot be avoided.
Further, in a case where the electron emitting device which is used in the image forming apparatus is a surface conducting type electron emitting device, in the introduction of the gas into the vacuum envelope in association with the activating step of the surface conducting type electron emitting device, the gas is introduced through the exhaust pipe into the vacuum envelope in which the face plate and the rear plate are adhered while keeping the distance therebetween to a few millimeters or less. There are, consequently, problems in manufacturing such as, that the conductance of the exhaust pipe and the vacuum envelope for the gas is small, it is difficult to obtain a constant pressure for a whole region in the vessel (vacuum envelope), it takes time until the pressure is stabilized, and the like.
(2) In the surface conducting type electron emitting device, after the activating step is performed, the gas used in the activating step and water, oxygen, CO, CO.sub.2, hydrogen, and the like are adsorbed to the electron source substrate or the material constructing the image forming apparatus, for example, the face plate having the fluorescent body. It is necessary to eliminate the adsorbed gas or the like in order to realize the stabilization of the electron emitting characteristics and to prevent a discharge by the remaining gas or the like. For this purpose, a step of exhausting through the exhaust pipe while baking the vacuum envelope after the seal bonding step, is needed.
According to the above step, however, since the conductance of the vessel and the exhaust pipe for the gas is small, the gas which is generated from the material cannot be always sufficiently exhausted and the stable electron emitting characteristics cannot be obtained, and there is a case of occurrence of a luminance fluctuation, decrease in life, and the like.
Further, a consistent manufacturing apparatus of the image forming apparatus which can solve the above problems and in which a re-contamination due to a readsorption of water, oxygen, hydrogen, CO, CO.sub.2, or the like to each of the degassed members does not occur, is demanded.
It is an object of the invention to provide an excellent manufacturing method and manufacturing apparatus of an image forming apparatus which can solve the foregoing problems, and to provide the image forming apparatus which is obtained by use of the manufacturing method and manufacturing apparatus.